Hi Mike, I would get someone over there to help you. A person who has a mechanical or electrical background. The instructions that come with that tach, they have no idea the vast array of modern aftermarket parts out there, as far as aftermarket and/or high-performance electronic ignition systems. The MSD boxes are very reliable. The MSD people have a 1-800 # as well as on-line support in the form of PDFs directions for all their MSD boxes. The coil wire negative RPM is for stock points ignition, that or a Pertronix One or Two. If you wire the tach up incorrectly it could damage the circuit board!!!!! There is an intense voltage spike at the "-" terminal of the coil on any low ohm Coil and or MSD controlled spark ignition system. That is why the MSD people give you a safe pre-amp RPM wire (or tab) that exits out the side of their red module. They are well aware that people would want to have a tachometer in these cars and the output RPM signal from the module is purpose made just for these cases.
I would take your car to a restoration shop that works on GTOs. The fuse block has extra tabs built-in for both battery power and Key on + power. If you wire that up wrong, it would be bad for your tach!!!
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Peter Serio
Owner, Precision Pontiac
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